In order to discuss the testability of the parameter region for the multi-step EWPT, we estimate the signal-to-noise (S/N) ratio for measurements of GW spectrum [1]}, [2]}.
The S/N ratio is defined as
\(S/N\,\, {\rm ratio} \equiv \sqrt{\delta \times t_{obs} \int ^{f_{max}}_{f_{min}}df \left[\frac{h^2 \Omega _{GW}(f)}{h^2\Omega _{Sens}(f)}\right]^2},\) 
